This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We started a new project, in collaboration with the Gary Blissard group at BTI Cornell, to investigate the role of the transmembrane (TM) domain of GP64 for viral membrane fusion. GP64 is the major glycoprotein in autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). Blissard and his coworkers found that mutants of GP64 in which the TM domain of GP64 was substituted with corresponding TM domains from six viral envelope proteins and two cellular membrane proteins could all induce hemifusion, but only some of the mutants could complete fusion activities. To examine what is the contribution of changes in the membrane structure to the differences in the fusion activities mediated by these proteins, the spin labeling method will be used to study the dynamic structures of plasma membrane vesicles (PMV) derived from sf9 cells in which GP64 and its mutants are expressed.